A. Field of Invention
This invention relates to coated machining tools such as drills, taps and milling cutters for metal forming and removal. Coating refers to the formation of a dry adherent or bonded layer on the surface of the tool. In particular, this invention pertains to the use of an energy source in forming a coating on the tool surface as a step in the machining sequence.
B. Prior Art
A basic machining sequence is used for the repetitive formation of drilled or threaded holes, or other machined formations (cuts), in a batch of parts, employing the use of a drill bit, or a tap, or a milling tool, or a broaching tool. For example, in a typical production sequence a part blank is fixed into position and a rotating drill or tap, or both, operates on the part to form certain required hole geometry or other machining operation. This tool is then retracted, the completed part replaced with another, and the drilling or tapping operation repeated. Although these steps comprise the basic machining sequence for batch machining, this simple process and the tools themselves can be augmented in many ways to accommodate specific aspects of a particular job. For example, depending upon the part material and desired operational speed, machining it can be a very abrasive and high friction operation, resulting in rapid tool wear and potential part or tool damage.
A large industry has grown up involved with improving tool performance and life. There is a great variety of machining fluids available to cool and lubricate during the machining process. Also, tools are available with a variety of specialty coatings applied during or after their manufacture for enhancing performance and tool life. It is observed in many situations that tool coatings out perform the sole use of xe2x80x98cuttingxe2x80x99 fluids, at least because an adherent or bonded coating is much more difficult to displace from the working tool surface than a fluid. For example, one can purchase drills, taps, and milling tools, etc. with no coating, with a titanium nitride coating (xe2x80x9cTiNxe2x80x9d), a titanium aluminum nitride coating (xe2x80x9cTiAlNxe2x80x9d), a boron carbide coating (xe2x80x9cBCxe2x80x9d), etc. Depending upon the material being machined and speed desired, these fluids and coatings can dramatically improve the operation.
However, coated tools are typically more expensive than uncoated tools, and the additional processing required to produce them can reduce availability, sometimes adding several days or (occasionally) weeks to delivery times. Even with coated tools, the machining process remains inherently abrasive, and tool coating durability becomes an issue. For example, a new TiN coated drill or tap may produce a perfectly acceptable result in a stainless steel part, at a particularly acceptable torque and speed, with excellent completed surface finish. However, as the number of holes completed by this tool increases, its coating wears, resulting in declining part quality. Also, the required torque increases until it is too high for the tool to sustain, risking tool breakage. Of course, besides the cost of the tool itself and parts scrapped, changing tools because of coating wear is also costly in downtime. What is needed is an apparatus and method to address the difficulties associated with tool coating wear.
The invention disclosed herein relates to a method of, and apparatus for, coating a machining (e.g. cutting tool) tool in a machine tool device, such as a lathe, drill, or milling machine. The primary object of this invention is to provide an apparatus and method which addresses and minimizes the difficulties associated with wear of machining tool coatings by refurbishing the tool coating on a regular basis, as often as in each machining cycle. Further objects and advantages are to provide such refurbishing apparatus and method which are easy to use, low in cost, and rapid in operation. Additional objects and advantages will become apparent from a consideration of the ensuing description and drawings.